1. Field of the Invention
The present invention relates to a display apparatus such as a projection display apparatus used for large-screen display of still picture or moving picture (video display), and so on.
2. Related Background Art
In recent years the variety of uses for the projection display apparatus have been increasing, for example, including display of an image of a computer in presentation with the computer, display of a video image of television, and so on, and there are thus demands for the display apparatus capable of gaining optimum chromatic purity, color balance, illuminance, etc. for a projected image in accordance with the uses.
FIG. 37 shows an example of the conventional projection display apparatus.
In FIG. 37, white light emitted from a lamp unit 100, which has a light source 101 and a reflector 102 for reflecting light from the light source, travels via fly's eye lens arrays 103 and 104, a polarization converting element array 105, a condenser lens 106, a total reflection mirror M0, etc. and thereafter is separated into light beams having their respective wavelength bands of red, green, and blue by dichroic mirrors DM1, DM2. The blue light travels via a reflection mirror M1 and a condenser lens 107B to enter an image display element 108B for blue image, the green light travels via a condenser lens 107G to enter an image display element 108G for green image, and the red light travels via a condenser lens 109, a reflection mirror M2, a relay lens 110, a reflection mirror M3, and a condenser lens 107R to enter an image display element 108R for red image. The color beams (color images) from the respective display elements are incident to a dichroic prism DP as an optical system for composition of colors to be combined into one, and the combined light of the three colors is magnified and projected onto an unrepresented screen or the like by a projection lens 111. On the screen a composite image (full color image) from the images displayed on the image display elements 108R, 108G, and 108B is formed as an enlarged image.
In FIG. 37 the light source 101 used herein is a discharge lamp such as a metal halide lamp, a mercury lamp, or the like.
FIG. 38 shows a spectral distribution of the discharge lamp as described above and the spectral distribution generally demonstrates a continuous intensity distribution in the wavelength band of the visible light ranging from 400 nm to 700 nm.
In the projection display apparatus of the aforementioned conventional example, if the wavelength band of 570 nm to 600 nm is taken into the green light when the color separation system including the dichroic mirrors DM1, DM2 separates the white light into the color beams of red, green, and blue, green will become yellow and thus the pure color of green will become hard to express. If the wavelength band of 570 nm to 600 nm is taken into the component of the red light otherwise, red will become orange and thus the pure color of red will become hard to express. For this reason, the apparatus is constructed to have dichroic filters or the like on the light incidence side of some image display elements, in addition to the dichroic mirrors DM1, DM2, and these filters eliminate the light in the wavelength band of 570 nm to 600 nm, so as to prevent the light component in the wavelength band of 570 nm to 600 nm from arriving at each of the image display elements for green and for red.
FIG. 39 is a spectral distribution of white light combined by the dichroic prism DP after the light in the wavelength band of 570 nm to 600 nm is eliminated.
FIG. 40A and FIG. 40B show spectral transmittances of the dichroic mirrors DM1, DM2 in the structure of the projection display apparatus of the aforementioned conventional example, and FIG. 41A and FIG. 41B show spectral transmittances of the dichroic filters DF1, DF2 necessary for elimination of the light in the wavelength region of 570 nm to 600 nm, where the dichroic filters DF1 and DF2 are placed on the light incidence side of the image display element 108G for green image and on the light incidence side of the image display element 108R for red image, respectively.
Moreover, Japanese Patent Application Laid-Open No. 7-72450 describes the projection display apparatus constructed in such structure that a dichroic filter, which reflects and blocks the light in the wavelength band of 570 nm to 600 nm but transmits the visible light except for the aforementioned wavelength band to direct it toward the image display elements as illustrated in FIG. 42, is interposed in an optical path between the light source and the dichroic mirror DM1 and that this dichroic filter is allowed to be moved into or out of this optical path, so as to switch between a state without use of the light in the wavelength band of 570 nm to 600 nm and a state with use thereof. Without use of the wavelength band, display of color image can be presented with priority to color reproducibility, because the chromatic purity is high. With use of the wavelength band, display of color image can be presented with priority to brightness, because the total light quantity increases.
Incidentally, the projection display apparatus described in the above Japanese application is constructed to control the image display elements by a fixed control pattern regardless of presence or absence of the dichroic filter. For this reason, the color reproduction was unnatural and the quality of image was degraded considerably in color images in the case of the brightness-priority display (without the dichroic filter).